In drive torque control, drive torque is calculated as the product of actual engine torque, the ratio, the drivetrain efficiency factor, and in the case of an automatic transmission, the converter amplification. Improved integrated control over actual engine torque and ratio is needed to cope with environmental requirements, such as, reductions of nitrogen oxides (NOx) emission and carbon dioxide (CO.sub.2) emission, without sacrificing ride feel. The integrated control can provide drive torque high enough to match the vehicle operator's desire as well as sufficiently low levels of NOx and CO.sub.2 emissions with excellent fuel economy. With the integrated control, transition response to the transmission may be improved by controlling the engine.
JP-A 10-148144 discloses an engine-transmission control system for a vehicle. The control system senses operator's desire relative to movement of the vehicle by measuring actual accelerator pedal angle. The actual pedal angle selects ratio to be established in the transmission and target engine torque. The engine throttle is controlled to adjust the actual engine torque toward the selected target engine torque.
U.S. patent application Ser. No. 09/325,795 was filed on Jun. 4, 1999 and assigned to the assignee of the present application, and is currently pending. A vehicular engine-CVT control system, which is disclosed by this U.S. patent application, senses operator's desire relative to movement of the vehicle and translates the sensed operator's desire into drive torque. In integrated control mode, the drive torque controls the engine throttle and the ratio of the CVT. Specifically, first target engine torque is calculated based on the drive torque, the converter amplification, and the CVT ratio. The control system has individual control mode where the integrated control is put out of operation. In the individual control mode, the sensed operator's desire controls the engine throttle, while the drive torque keeps on controlling the ratio of the CVT. Specifically, the sensed operator's desire determines second target engine torque. The control system provides a control over the transition period over the integrated and individual control modes. The first engine torque is used as a first input to and the second engine torque is used as a second input to a transition controller. The transition controller calculates a final target engine torque as the sum of the first product of (1-K) and the second target engine torque and the second product of K and the first target engine torque. The character K is a coefficient that varies linearly between 0 and 1 within a predetermined period where the magnitude of a difference between the first engine torque and the second engine torque is unaltered. In the individual control mode, the coefficient K is 0 so that the final target engine torque is as high as the second target engine torque. In the integrated control mode, the coefficient K is 1 so that the final target engine torque is as high as the first target engine torque. During transition period, the coefficient K varies from 0 to 1 for a shift from the individual control mode to the integrated control mode, and it varies from 1 to 0 for a shift from the integrated control mode to the individual control mode. The final target engine torque controls the engine throttle.
This control system is fairly well developed. However, a need remains for further development of such system, especially in light of current movement to an integrated vehicular power train control system.